.box{
    width: 80%;
    height: 100px;
    margin: 0%;
    border: 2px solid red;
}

/* .pos_static{

} */

.pos_relative{
    position: relative;
    background: yellow;
    top: 20px;
    left: 20px;
    z-index: -1;
}

.pos_absolute{
    position: absolute;
    background: purple;
    z-index: -10px;
    top:10px;
    left: 10px;
}

.parent_absolute{
    position: relative;
    /* position: absolute; */
}

.pos_fixed{    /* 回到顶部图标 */
    position: fixed;
    background: brown;
    /* top: 0; */
    /* left: 0; */
    right: 0;
    bottom: 20px;
    width: 10%;
}

.pos_sticky{    /* 具有位置可变化，又可被固定位置的特点 */
    position: sticky;
    background: firebrick;
    top: 200px;
}